The behavioral and synaptic functions of serotonin are being investigated in a terrestrial mollusk, the giant garden slug Limax maximus, by focusing on the synaptic inputs and outputs of a pair of large identified neurons in the cerebral ganglia called the metacerebral giant cells (MGC). The MGCs are known to modulate feeding behavior under some conditions and therefore interactions between the MGCs and the neural network that generates feeding motor program is being studied. Drugs known to be serotonin agonists were applied to the isolated brain and their effect on the feeding network determined. To further define the feeding network and cells synaptically activated by the MGCs, we have developed techniques to use tritiated 2-deoxyglucose as a marker of neuronal electrical activity with clean cellular resolution in the autoradiographs. We are also examining the effects of enhanced dietary intake of transmitter precursors such as tryptophane and choline on learning and retention of an associative memory.